This invention relates to low-sulfur consumable lubricating oil compositions and to a method of operating an internal combustion engine using the same. The inventive method provides the advantage of extending required time intervals between oil changes and reducing NOx levels in exhaust gases.
A problem associated with internal combustion engines equipped with exhaust gas aftertreatment devices (e.g., catalytic converters, particulate traps, catalyzed traps, etc.) is that the lubricating oils for such engines are used in both the crankcase as well as in high wear areas such as the valve train. Because these oils are used in high wear areas they usually contain extreme pressure (EP) agents which typically contain metal (e.g., zinc) and phosphorus in order to be effective. During the operation of the engine these EP agents decompose and the resulting decomposition products eventually enter the aftertreatment device resulting in damage to the device. The problem therefore is to provide a lubricating oil composition that avoids damaging the exhaust gas aftertreatment device.
Another problem associated with conventional internal combustion engines is that the time interval required between oil changes typically is less than the time interval required for other service items such as air filter replacements, coolant changes, brake replacements, and the like. Oil changes are viewed as one of the most aggravating and, in some cases, most costly maintenance aspects of vehicle ownership. Traditionally, oil change intervals have been extended by base stock and additive upgrades. Since the 1920s, for example, the extensions have been about 15xc3x97 or greater. Regardless of this progress, the time intervals required between oil changes continue to lag behind the time intervals required for other service items. The problem therefore is to improve the lubricant technology for these engines so that the time intervals between oil changes can be extended to coincide with other service intervals.
Another problem associated with the operation of internal combustion engines is that the exhaust gases from such engines contain NOx which is an undesirable pollutant. It would be advantageous if the level of NOx in the exhaust gases of internal combustion engines could be reduced.
The present invention provides a solution to each of these problems. With the present invention low-sulfur consumable lubricating oil compositions characterized by the absence of EP agents containing metal and phosphorus are used and as a result the exhaust gas aftertreatment device is protected from harmful exposure to such EP agents or their decomposition products. In accordance with the inventive method, the required oil change intervals are extended due to the fact that during operation of the engine, used engine oil is continuously or periodically removed from the engine and replaced with new oil. Unexpectedly, the levels of NOx in exhaust gases from engines operating in accordance with the inventive method are reduced.
U.S. Pat. No. 5,955,403 discloses a sulfur free lubricating oil composition which comprises a major portion of a synthetic base lubricating oil and a minor portion of a tri(alkyl phenyl) phosphate or di(alkylphenyl) phosphoric acid antiwear agent, an amine antioxidant a substituted succinamide rust inhibitor, and a tolyltriazole. The tri(alkylphenyl)phosphate antiwear agent is incorporated in the oil in an amount ranging between about 0.1 to 2.0 wt % and the amine antioxidant in amount ranging from about 0.1 to 5 wt %. The succinamide is present in an amount ranging from about 0.01 to 0.5 wt %, and the tolyltriazole from about 0.01 to 0.5 wt %.
U.S. Pat. No. 4,392,463 discloses a diesel engine having a first lubrication system, containing conventional engine oil, used to lubricate that section of the engine subjected to excessive wearxe2x80x94the valve train including the cam shaft, valve lifters, rocker arm, valve stems, etc., and a second lubricant system, utilizing diesel fuel, for lubricating the remaining section of the enginexe2x80x94the crankshaft and associated parts, pistons, connecting rods, etc. By being exposed to crankcase blowby exhaust gases, diesel fuel used to lubricate the crankshaft, etc. absorbs pollutants and contaminants contained therein and recirculates these contaminants through the fuel system to be burned and exhausted. By constantly being lubricated with fresh lubricant, wear on these specific parts is reduced. The reference indicates that frequent lubrication changes have been eliminated because the diesel fuel/lubricant is continuously changed and circulated through the fuel system. Since the engine oil and the first lubrication system is not exposed to crankcase blowby exhausted gases, its useful life is prolonged, thus reducing the frequency of required oil changes.
This invention relates to a low-sulfur consumable lubricating oil composition, comprising: a base oil; an acylated nitrogen-containing compound having a substituent of at least about 10 aliphatic carbon atoms; and a sulfur content of about 5 to about 250 ppm; said composition being characterized by the absence of an extreme-pressure additive containing metal and phosphorus.
This invention further relates to a a method of operating an internal combustion engine equipped with an exhaust gas aftertreatment device, said method comprising:
(A) operating said engine using a normally liquid or gaseous fuel;
(B) lubricating said engine using the foregoing low-sulfur consumable lubricating oil composition;
(C) removing part of said low-sulfur consumable lubricating oil composition from said engine, said removed part of said low-sulfur consumable lubricating oil composition (i) being combined with said fuel and consumed with said fuel as said engine is operated or (ii) being combined with the exhaust gas from said engine and removed from said engine with said exhaust gas; and
(D) adding an additional amount of said low-sulfur consumable lubricating oil composition to said engine to replace said removed part of said low-sulfur consumable lubricating oil composition.